There is a trick, or technique I should call it, for dealing with the well-known cliche: Slightly change it.

1. Opportunity only knocks once.
2. This opportunity would knock only once.

Does #2 completely avoid the cliche? No. But for me, the annoying part of being a cliche went away with just that small change.

There's something else to notice: I made it more accurate. (That's the second time I have suggested that metaphicals should be accurately descriptive.) Using a cliche in its original form has a tendency to be thoughtless, and changing it in some random way is still be thoughtless. But making it right, that takes thought. (Above, it was only that particular opportunity she would never get again.)

1. That opens Pandora's box.
2. That opens a Pandorian box.

I would have been perfectly content with that cliche, except it wasn't quite right – I didn't want all of the associations to Pandora's box. So I made up a word, got a vaguer meaning, and as a side benefit I avoided the cliche.

I see a big smile with a lot of bright teeth, somehow reminding me of the wolf in Little Red Riding Hood.

I can see how they're slowly conditioning me. But I can't stop it. If there are any frogs swimming in hot water, they should be really frightened by the story of what's happening to me.

My hand is the Tyrannosaurus Rex in the room.

I wanted the meaning of deadly predator.

A popular senior has stopped to talk to her. After he leaves:

I pinch my arm, and I can feel it. So that wasn't a dream.

I pinch my arm, and I can't feel it. But that was too strange to be a dream. ("Lida and SexySleepwalker")

That riffs on the idea of pinching yourself to see if you are dreaming – if it hurts, you aren't.

Instead of saying time passed slowly:

Time passes again. I don't know how long. I had no watch. They don't make that kind of time in watches anyway. (Farewell, My Lovely, Chandler, page 171 in paperback)